In compressed air discharged from a pneumatic compressor such as an air compressor, drain which is condensed water or dust, or impurity such as lubricant oil used in the pneumatic compressor is included. Since the compressed air is thereafter used for a pneumatic apparatus such as an air gun or a cylinder, inclusion of such impurity could cause malfunction etc. of the pneumatic apparatus. That is, there is a possibility that inclusion of impurity becomes harmful to a future use of compressed air. Consequently, impurity in compressed air is separated or removed from the compressed air appropriately via an air filter (for example, see JP-A-Hei 6-315615).
In a compressed air pressure circuit where compressed air flows, if there is a sufficient space in a place for locating an air filter as in JP-A-Hei 6-315615, it is possible to use a large-sized air filter to improve filter efficiency. However, there is a case where this space is large enough only in the upper and lower directions, and not large enough in the right and left directions. In such a case, use of an air filter which efficiently utilizes a space in the upper and lower directions is preferable. As such a filter, there is one in which filters are respectively provided in the upper and lower directions to an inflow direction and an outflow direction of compressed air (for example, see JP-A-2014-237094).